United States and the Paris Agreement

In April 2016, the United States became a signatory to the Paris Agreement on climate change mitigation, and accepted it by executive order in September 2016. President Obama committed the United States to contributing US$3 billion to the Green Climate Fund. On June 1, 2017, U.S. president Donald Trump announced that the United States would cease all participation in the 2015 Paris Agreement on climate change mitigation, contending that the agreement would "undermine" the U.S. economy, and put the U.S. "at a permanent disadvantage".

In accordance with Article 28 of the Paris Agreement, a country cannot give notice of withdrawal from the agreement within the first three years of its start date in the relevant country, which was on November 4, 2016, in the case of the United States. The White House later clarified that the U.S. would abide by the four-year exit process. On November 4, 2019, the administration gave a formal notice of intention to withdraw, which takes 12 months to take effect. The withdrawal took effect on November 4, 2020, one day after the 2020 U.S. presidential election. However, the U.S. still has to report its greenhouse gas inventory because it remains in the UNFCCC.

The decision to withdraw the U.S. was backed by many Republicans but was strongly opposed by Democrats. However, it was strongly criticized in the U.S. and abroad by environmentalists, religious organizations, business leaders, and scientists. According to polls released in 2019, a majority of Americans opposed the withdrawal. Following Trump's announcement, the governors of several U.S. states formed the U.S. Climate Alliance to continue to advance the objectives of the Paris Agreement at the state level despite the federal withdrawal. As of July 1, 2019, 24 states, American Samoa, and Puerto Rico have joined the alliance, and similar commitments have also been expressed by other state governors, mayors, and businesses. The withdrawal from the Paris agreement impacted other countries by reducing its financial aid to the Green Climate fund. The termination of the $3 billion U.S. funding ultimately impacted climate change research and decreased society's chance of reaching the Paris Agreement goals, as well as omitted U.S. contributions to the future IPCC reports. It also affected the carbon emission space as well as the carbon price. The U.S.'s withdrawal also meant that the spot to take over the global climate regime was obtainable for China and the EU.

Following the 2020 presidential election, President-elect Joe Biden vowed to rejoin the Paris Agreement on his first day in office. On January 20, 2021, shortly after his inauguration, President Biden signed an executive order to rejoin the agreement. The United States formally rejoined the Paris Agreement on February 19, 2021, 107 days after the withdrawal took effect. On January 20, 2025, shortly after his second inauguration, President Trump signed an executive order to withdraw the United States from the agreement for a second time.